The present invention relates to an acidic amorphous silica-alumina having a large specific surface area and a large pore volume, a carrier complex and a hydrotreating catalyst containing the same, in particular a hydrocracking catalyst containing the acidic amorphous silica-alumina in combination with a modified zeolite-Y for treating petroleum hydrocarbon materials to produce middle distillates, and processes for the preparation thereof.
The amorphous silica-alumina, as one of the important support components of catalysts, is required to have an adequately large specific surface area and large pore volume to support active metal components. Additionally, the amorphous silica-alumina also needs generally to provide a certain acid cracking function for efficient reaction. However, none of the disclosed products of the prior arts possesses both functions. Commonly, the amorphous silica-alumina used as an acidic component should be dispersed in a matrix of refractory oxides having a large specific surface area and a large pore volume, such as a large pore alumina, which may serve jointly as a catalyst support. Due to limitations in the preparation processes of the prior art, when an amorphous silica-alumina which is required to have a desired pore structure that can be used directly as a catalyst support is prepared, silica introduced into it cannot be sufficient, and consequently the number of acid sites is low; on the other hand, if sufficient silica is added to increase the number of acid sites, it is liable to crystallize and will cause damage to the pore structure. Particularly, with respect to the mid-distillate type hydrocracking catalyst, in addition to the activity of the catalyst, its mid-distillate selectivity should be especially taken into consideration. Thus, in addition to a certain amount of acid sites, the carrier component is required to have comparatively good properties in respect of pore structure, including a layer specific surface area and more effective pore volume to improve the dispersion of active metal components in the carrier and to modify the diffusion properties in tje coursr of reaction. The application of zeolite component in catalysts enhances the activity level of the catalysts, in particular that of the hydrocracking catalysts. The application of zeolite component in catalysts marks a great progress in the field of hydrocracking catalyst as compared with the catalysts comprising solely amorphous silica-alumina. Zeolite is first applied in light-distillate type hydrocraking catalysts, and latter in mid-distillate type hydrocracking catalysts. However, with respect to a mid-distillate type hydrocraking catalyst, the activity may not be the most important element to be considered, but the mid-distillate selectively is very important. It is true, that a large amount of zeolite can enhance the cracking activity of the catalyst, but its excessively strong cracking activity may result in noticeable decrease in the mid-distillate selectivity. Therefore, it needs to seek a better balance between the activity and the mid-distillate selectivity of the catalyst.
GB 2166971A discloses a silica-alumina cogel having a specific surface area of 100-400 m2/g, of which 30-60% is contributed by the pores having a diameter of about 4-10 nm, and a process for the preparation thereof, comprising first mixing an alkali metal aluminate and silicate to obtain a mixture having a pH of about 12 to 12.5, and then reacting the mixture with aluminum sulfate to obtain the resultant product. From the examples of the application, it can be learned that the typically resultant product SiO2xe2x80x94Al2O3xe2x80x94Re2O3 cogel has a specific surface area of 277 m2/g, a pore volume of 0.31 ml/g and an average pore diameter of 6.1 nm respectively under the conditions that its SiO2 content is less than 35 wt %. Although the said product possesses cracking activity, it has the defects of being small in pore volume and specific surface area and cannot be used as a carrier alone for supporting a large amount of metal components.
U.S. Pat. No. 4,758,330 discloses a catalyst composition having a high surface area and a high pore volume comprising alumina as the major component and silica as a minor modifying component, and also discloses a process for preparing an amorphous silica-alumina by first preparing an alumina hydrogel by pH swing preparation in a range of 2 to 10, and then adding to the hydrogel a silicate to obtain the amorphous silica-alumina. The process is complicated in operation and difficult to control, and moreover the obtained product has a low SiO2 level (less than 8.7 wt %), so it is generally used as a carrier of a hydrofining catalyst, which is not required to have the function of acidic cracking. Although this product has a pore volume of up to 1.78 ml/g, its pore volume is contributed substantially by large pores of 10-10 nm, and only 0.31 ml/g by pores of 3-10 nm, and this product has a specific surface area of 308 m2/g.
EP 0,228,270 describes a process by which alumina is treated with sodium silicate or silica sol, and is then subjected to hydrothermal treatment to improve the properties of the amorphous silica-alumina and to give the final amorphous silica-alumina having a SiO2 content of 6-12 wt %. In an embodiment of the invention, the alumina is treated with a silica sol, and then the resultant amorphous silica-alumina containing 12 wt % of SiO2 is treated by a hydrothermal method in order to give a product having the highest specific surface area, however, even in this case, the specific surface area is only 214 m2/g. The operational conditions of the process described above are rigorous and energy consumption in the hydrothermal treatment is large.
U.S. Pat. No. 4,517,074 discloses a hydrocracking catalyst for producing 300-700xc2x0 F. (149-371xc2x0 C.) middle distillates, wherein the feedstocks are preferably pretreated by hydro-denitrogenation and/or hydro-desulfurization. Said catalyst is characterized in that it comprises, in addition to a zeolite component, a dispersion of SiO2xe2x80x94Al2O3 in alumina matrix, wherein the amorphous silica-alumina having a certain level of cracking activity has to be dispersed into an alumina matrix, such as large-pore xcex3xe2x80x94Al2O3 used as a component of the carrier, so as to obtain sufficient pore volume and specific surface area for supporting a large amount of metal components for hydrogenation. according to its embodiment example, the activity of catalyst is relatively low, thus, in order to achieve a conversion of 60 vol %, the reaction temperature must generally be higher than 400xc2x0 C. While the reaction temperature is still needed to be kept at 389xc2x0 C. even though an example of the patent showed that by the use of a catalyst comprising a silica-alumina containing as high as 75% of silica dispersed in xcex3xe2x80x94Al2O3 in combination with a zeolite, such as zeolite LZ-10.
Therefore, there is still a need in the art to develop a hydrocracking catalyst having both good activity and high mid-distillate selectivity, and a process for the preparation thereof.
After extensive studies and experiments, the inventors have invented an acidic amorphous silica-alumina having a large specific surface area and a large pore volume and a process for the preparation thereof. When used as a carrier component, preferably in combination with a zeolite-Y, the acidic amorphous silica-alumina will provide a hydrocracking catalyst with the desirable properties including both good activity and high mid-distillate selectively.
An object of the present invention is to provide an amorphous silica-alumina having a large specific surface area and a large pore volume and an adequate content of SiO2 to ensure a desired acid function for chemical reactions, which is particularly useful as a carrier component in the preparation of a hydrocracking catalyst having both good activity and high mid-distillate selectivity.
Another object of the present invention is to provide a carrier complex comprising an acidic amorphous silica-alumina of the present invention, which is particularly useful as carrier component in the preparation of a hydrocracking catalyst having both good activity and high mid-distillate selectivity for producing mid-distillate.
A further object of the present invention is to provide a hydrocracking catalyst, comprising hydrogenation metal components, a specific amorphous silica-alumina, and optionally a crystalline compound including a zeolite, which has both good activity and high mid-distillite selectivity and is particularly useful in treating heavy hydrocarbon materials to produce middle distillates.
Anther still further object of the present invention is to provide a hydrocracking catalyst, comprising hydrogenation metal components, a specific amorphous silica-alumina, and a modified ultrahydrophobic zeolite-Y, which has both good activity and high mid-distillate selectivity and is particularly useful in treating heavy hydrocarbon materials to produce middle distillates.
A still further object of the present invention is to provide a process for the preparation of an acidic amorphous silica-alumina having a large specific surface area and a large pore volume, with simplified procedures and lower costs for starting materials and lower energy consumption.
Still another object of the present invention is to provide a process for the preparation of the catalyst of the present invention, comprising the steps of mixing a specific amorphous silica-alumina, optionally a crystalline compound including a zeolite, and optionally a binder, kneading, rolling, pressing and moulding into carrier, and then supporting active hydrogenation metals onto said carrier to obtain the catalyst of the invention.
These and other objects of the present invention will become apparent to the person skilled in the art after reading the specification.
The silica-alumina according to the present invention is substantially amorphous and has a SiO2 content of 10-50 wt %, a specific surface area of 300-600 m2/g, a pore volume of 0.8-1.5 ml/g, and an acidity measured by an infrared method (conducted by an acidimeter Necolet 550, herein after referred to as IR acidity) of 0.25-0.60 mmol/g.
Preferably, the amorphous silica-alumina according to the present invention has a SiO2 content of 15-50 wt %, and more preferably 20-40 wt %.
Preferably, the amorphous silica-alumina according to the present invention has a specific surface area of 350-600 m2/g more preferably 400-550 m2/g, and most preferably 450-500 m2/g.
Preferably, the amorphous silica-alumina according to the present invention has a pore volume of 0.9-1.4 ml/g, more preferably 1.0-1.4 ml/g, and most preferably 1.0-1.3 ml/g.
Preferably, the amorphous silica-alumina according to the present invention has an IR acidity of 0.30-0.55 mmol/g, more preferably 0.35-0.50 mmol/g, and most preferably 0.40-0.45 mmol/g.
The amorphous silica-alumina according to the present invention may optionally contains phosphorus, preferably of 1-5 wt % calculated as P2O5.
According to the present invention, the amorphous silica-alumina is prepared by a process with parallel flows and a fixed pH. The principle of the preparation of the amorphous silica-alumina according to the present invention is based on that a pre-matrix of alumina is formed first and an appropriate initiative heterogeneous crystal form, which will shift to amorphourous statein the following step, is obtained by controlling the neutralization conditions as described below, then the positions of aluminum atoms are replaced by silicon atoms. This is different from the processes of the prior arts in which alumina is impregnated with silicon source and the silicon atoms simply precipitate onto alumina, thus the acidity cannot be greatly increased and the pores in the support will be damaged. Unlike the process of the prior arts in which the amount of silicon added will influence considerably the specific surface area and pore volume of the final products, the process of the present invention can form an amorphous silica-alumina with a high specific surface area and a large pore volume, even if the silica level of the product varies in a very wide range. The preparation of the amorphous silica-alumina of the present invention features that aluminum atoms are attacked and replaced by silicon atoms in a prevailing concentration in a short time, thereby forming the skeletons of a large number of original acid sites, which manifest substantially the feature of Lewis acid owing to the presence of free aluminum and the subsequent amorphous transformation. Then, the replaced aluminum atoms enter into the sol system, together with excess aluminum atoms in the system, form continuously new colloidal particles which interact with the germinal Al2O3 and SiO2, while germinal silica-alumina grow and aggregate to form larger colloidal particles. Under a certain aging condition, the crystalline growth is destroyed for transformation into amorphous form is undergoing. With the above-described features, the amorphous silica-alumina of the present invention has not only a higher acidity, but also a higher specific area and a large pore volume because of a high level of amorphism as compared with the products of the prior arts in this field. Thus, the amorphous silica-alumina of the present invention needs not to undergo further hydrothermal treatment or other methods for enlarging the pores.
The amorphous silica-alumina according to the present invention can be prepared in the following steps:
(a) adding in parallel flows an acidic aluminum salt solution and a basic precipitant solution, or a basic aluminum salt solution and an acidic precipitant solution, into a reactor containing a small amount of de-ionized water and carrying out the neutralization reaction to form a colloidal sol;
(b) optionally stabilizing the resulting sol from step (a);
(c) adding a silicon compound to the resultant from step (b);
(d) aging the mixture from step (c);
(e) filtering and washing the resultant from step (d); and
(f) where necessary, adding a phosphorous compound, filtering the resultant; and
(g) drying the resultant (e) or (f) and crashing it to obtain the amorphous silica-alumina product.
In the process for preparing the amorphous silica-alumina as described above, the acidic aluminum salt may be any soluble acidic aluminum salt which can react with a basic precipitant to form an appropriate colloidal sol of alumina, and is preferably selected from the group consisting of Al2(SO4)3, Al(NO3)3 and AlCl3, and in the industrial application Al2(SO4)3 is more preferably used because of its low price; the basic precipitant may comprise any soluble base, for example, an alkali or alkali earth metal hydroxide, carbonate, bicarbonate, aluminate, aqueous ammonia, etc., and is preferably selected from the group consisting of NaOH, NH4OH and NaAlO2. In the case that a basic aluminum salt and an acidic precipitant are used in step (a), said basic aluminum salt may be a soluble alkali and alkali earth metal aluminate, preferably in alkali metal aluminate and more preferably sodium aluminate (NaAlO2); and said acidic precipitant may be an acidic aluminated such as Al2(SO4)3, Al(NO3)3 and AlCl3 or inorganic acid such as hydrochloric acid, sulfonic acid and nitric acid, or an organic acid such as sulfonic acid and carboxylic acid such as formic acid and acetic acid, and an acidic material as defined above for the acidic aluminum salt, etc. In general, different precipitants will make the alumina matrix obtained from step (a) different in particles sizes. The basic precipitants which can lead to different sizes of alumina colloidal particles are listed in the following order based on the resultant particle sizes: NaOH less than NaAlO2 less than NH4OH. The said silicon compound used in step (c) may be any organic silicon compound which can introduce silica to produce the amorphous silica-alumina product, and is preferably selected from the group consisting of silicate, waterglass, a silica sol and other silicon compounds, more preferably sodium silicate, waterglass and silica sol. In the process of this invention, different precipitants can be used for preparing the amorphous silica-alumina of the present invention having properties within the desired ranges. To meet the different requirements of various catalytic reactions, these products with different pore diameters and pore distribution can be obtained by adjusting the reaction conditions.
The acidic amorphous silica-alumina having a high specific surface area and a large pore volume and having desired properties can be obtained under different conditions described below. The silica- alumina product having different pore diameters and pore distribution resulted from the change in conditions may be used in various catalytic reactants and reaction types. And for different purposes of use, various amorphous silica-alumina having different acidic cracking functions may be required, and such an amorphous silica-alumina having a certain level of acidity and cracking activity can be prepared by adjusting the amount of silicon compound added in the course of the preparation. Contrary to the prior art process in which the amount of added silicon compound will obviously affect the specific surface area and pre volume of the product, the process according to the present invention can provide an acidic amorphous silica-alumina having a high specific surface area and a large pore volume in a very wide range of SiO2 content. For example, when the amorphous silica-alumina product of the present invention has a 45 wt % SiO2 content, it still included in the scope of the present application.
In step (a) of the above process, the addition can be operated at room temperature; the starting solutions can be added in an appropriate concentration, for example, the acidic aluminum salt solution can be used at a concentration of 4-20 g/100 ml, and as a basic precipitant, for example, sodium aluminate can be used at a concentration of 10-30 g/100 ml and aqueous ammonia at about 8-12 v %, and the neutralization reaction can be carried out at a temperature of 50-80xc2x0 C., a pH value of 6.0-10.0 or a sufficient period of time, for example, for 0.5-2 hrs, preferably 1-2 hrs.
In step (b), the stabilization can be carried out at room temperature and a pH value of 6-9 for a sufficient period of time, for example, for 0-60 mins.
In step (c), because of the features and mechanism of the preparation process according to the invention as described above, the addition of silicon compound into the resultant from step (b) should be completed in a short time so as to ensure that in a certain period a prevailing concentration of silicon ions can be obtained to attack the alumina pre-matrix formed in this reaction system. Of course, the adding period cannot be too short regarding to the efficiency of mass transfer under stirring. The adding period is preferably 5-20 mins.
After a silicon source is introduced, the pH value in this system will be subjected to a changing course, showing that amorphous silica-alumina starts being formed on the alumina matrix. After the reaction equilibrium is achieved, the appropriate conditions should continuously be maintained to complete step (d). This procedure is an aging process in a broad sense, that is, the procedure comprises both the step of forming amorphous silica-alumina in the reaction and the subsequent step of amorphous transforming of the resultant. In this step, the aging can be carried out at a pH value of 7.5-9.5, and a temperature of 50-70xc2x0 C. for 0-60 mins.
After aging, the steps (e) and (g) can be carried out in a conventional way, that is, the resultant amorphous silica-alumina is washed to remove impurities such as iron ions, sodium ions, sulfate ions, chloride ions, etc., and then dried and crashed to give the amorphous silica-alumina of the present invention. The purpose of removing the impurities is to ensure that the impurities in amorphous silica-alumina will be reduced to such a level that they cannot affect the activity and stability of the catalyst when the amorphous silica-alumina according to the invention is used as a catalyst support or an acidic component of the catalyst.
The amorphous silica-alumina of the present invention can be dried in an oven or by spraying, for example, dried in an oven at a temperature of 90-120xc2x0 C., preferably about 110xc2x0 C. for 6-10 hrs, to make the dry matrix of the amorphous silica-alumina produced be up to 60-80 wt %. Then, the dried amorphous silica-alumina is sieved into preferably smaller than 150 mesh, more preferably smaller than 200 mesh.
The amorphous silica-alumina of the present invention may optionally comprise 1-5 wt % of phosphorous (calculated as P2O5) in order to improve the distribution of pore diameters and the said phosphorus may also have delicate effects on the properties of a catalyst containing the amorphous silica-alumina. Said amorphous silica-alumina containing phosphorus can be obtained by slurrying again the above amorphous silica-alumina, adding a proper amount of phosphorous compound such as phosphoric acid, so that the product contains 1-5 wt % P2O5 based on the total weight of the amorphous silica-alumina, then filtering, drying and crashing to give the product containing phosphorous.
The amorphous silica-alumina mentioned above may be used alone or in combination with a crystalline compound including a zeolite component, optionally alumina and optionally other refractory oxides as a carrier. Therefore, the present invention further provides a carrier complex containing the amorphous silica-alumina having a dual-function as a component, which comprises:
(a) 10-90 wt % of the amorphous silica-alumina according to the present invention,
(b) 0-60 wt % of a crystalline compound including a zeolite component, and
(c) 0-60 wt % of an alumina and/or other refractory oxides.
Preferably, the carrier combination according to the present invention comprises:
(a) 15-80 wt % of the amorphous silica-alumina according to the present invention,
(b) 5-50 wt % or a crystalline compound including a zeolite component, and
(c) 5-50 wt % of an alumina and/or other refractory oxides.
Preferably, the carrier combination according to the present invention comprises:
(a) 20-70 wt % of the amorphous silica-alumina according to the present invention,
(b) 10-40 wt % of a crystalline compound including a zeolite component, and
(c) 10-40 wt % of an alumina and/or other refractory oxides.
Where the carrier complex mentioned comprises no component (b), it should comprises (c), and where it comprises no (c), it should comprises (b). The alumina used in the carrier complex of the present invention can be either a large pore alumina or a small pore alumina, preferably a small pore alumina, and more preferably, a small pore alumina which is peptized with nitric acid and has a specific surface area of 240-280 m2/g and a pore volume of 0.4-0.5 ml/g.
The refractory oxide optionally used in the carrier complex according to the present invention may be any mentioned the following, for example, zinc oxide, zirconium oxide, titanium oxide, magnesium oxide, and the like.
The crystalline compound used as a component of the complex include a various kinds of crystal alumisilicate and zeolites. Those zeolites which are commonly used as a component in the catalyst of the art, including zeolite-Y, zeolite-xcex2, zeolite-ZSM, zeolite-SAPO, etc. may also be used in the carrier complex. The zeolite used in the carrier combination is preferably a zeolite-Y, and more preferably a modified ultra-hydrophobic zeolite-Y.
Most preferably, the ultra-hydrophobic zeolite-Y used in the carrier complex according to the invention has an SiO2/Al2O3 molar ratio of 5-25, and IR acidity of 0.2-0.6 mmol/g and absorptive capacity for water vapor of less than 5 wt % at 25xc2x0 C. and P/P0 of 0.1. Preferably, said ultra-hydrophobic zeolite-Y has a SiO2/Al2O3 molar ratio of 6.0-17; and has an appropriate proportion of non-skeletal alumina, which accounts for 10-50 wt % based on the total weight of alumina contained in the zeolite; a very narrow range of crystal unit cell size, generally between 2.420 and 2.445 nm, most preferably between 2.425 and 2.435 nm. The ultra-hydrophobic zeolite-Y most preferably used in the carrier complex according to the present invention has obviously secondary pores, that is, the modified zeolite-Y has an increased number of pores, accompanied by the increase in specific surface area and pore volume. Said zeolite-Y has a specific surface area of 600-850 m2/g, preferably 700-800 m2/g; a pore volume of 0.2-0.6 ml/g, preferably 0.3-0.5 ml/g, with more than 50% of the total pore volume being contributed by the secondary pores have diameters of over 2 nm, and an IR acidity of preferably 0.25-0.55 mmol/g.
The carrier complex of the present invention can be prepared by mixing 10-90 t % of the amorphous silica-alumina according to the present invention, 0-60 wt % of a crystalline compound including a zeolite component, and 0-60 wt % of an alumina and/or other refractory oxide, kneading, rolling and pressing the blend into block mass, and extrusion moulding the block mass by an extruder into carrier bars to obtain the carrier complex of the present invention.
The moulded carrier bars may be in any suitable shape, for example, in a cylindrical shape having a diameter of 1.2-1.8 mm, or in the specific shapes, such as trefoil or quatrefoil in cross-section. The moulded carrier bars can be dried at a temperature of 90-160xc2x0 C., preferably 110-140xc2x0 C. for 6-12 hours, preferably 8-10 hours, and activated by calcination at a temperature of 400-650xc2x0 C., preferably 450-600xc2x0 C. for 1-10 hours, preferably 3-6 hours to obtain the carriers ready for use.
The modified ultra-hydrophobic zeolite-Y most preferably used in the carrier complex according to the invention may be prepared in the following steps:
(1) preparing a zeolite-Y having a Na2O content of less than 0.2 wt %;
(2) adding the zeolite-Y to a calcining oven, calcining at 450-700xc2x0 C. and under a pressure of 0.01-1.0 MPa of water vapor produced on-site or additionally introduced, for 0.5-10 hours to obtain an ultra-hydrophobic zeolite-Y having a SiO2/Al2O3 molar ratio of 5.2-6.0.
The ultra-hydrophobic zeolite-Y obtained according to the above steps may be further dealuminzed selectively by a chemical method to obtain an ultra-hydrophobic zeolite-Y having a SiO2/Al2O3 molar ratio of 6.5-25. The chemical method for the selective dealuminization is carried out to remove selectively the non-skeletal alumina in the zeolite with a solution of an acid, such as hydrochloric acid, nitric acid, acetic acid, oxalic acid and the like, or of an organic complexing agent, such as acetylacetone, EDTA and the like.
And the zeolite-Y having a Na2O content of less than 0.2 wt % can be prepared according to the following methods of (a) or (b):
(a) stirring a commercial zeolite NaY as starting material in an ammonium ion-exchanging solution having a concentration of 1.0-5.0M, preferably 2.0-3.0M, in which the concentration of the zeolite NaY is 0.05-1.0 g/ml, preferably 0.1-0.5 g/ml, at a temperature of 70-150xc2x0 C., preferably 80-120xc2x0 C., for 0.5-3 hours, and repeating the above ion-exchange step again and again till a zeolite-Y having a Na2O content of less than 0.2 wt % is obtained.
(b) ion-exchanging a commercial starting material zeolite NaY according to the same ion-exchanging method as mentioned in (a) for 2-3 times to obtain the zeolite-Y product having a Na2O content of less than 3.0 wt %, which is then hydrothermally treated at 450-600xc2x0 C. and under a vapor pressure of 0.01-0.2 MPa for 0.5-3 hours; then ion-exchanging the resulting zeolite-Y by the same ion-exchanging method as mentioned in (a) for 2-3 times to obtain the zeolite-Y having a Na2O content of less than 0.2 wt %.
The carrier complex according to the present invention can be used alone directly as a carrier of a catalyst which needs a carrier having a certain degree of acidity function and having large specific surface area and pore volume to support its active metal component, in particular, a carrier of a catalyst for acidic catalytic reaction such as those for hydrocracking of petroleum hydrocarbon materials to produce middle distillates. Accordingly, the present invention further provides a catalyst comprising an active metal component and the carrier combination according to the present invention as carrier component.
In the case that the carrier complex consists of the amorphous silica-alumina of the present invention. And the amorphous silica-alumina of the present invention can be used directly as a support component with a large pore volume and a large specific surface area, as well as with a certain function for acidic cracking. Since the amorphous silica-alumina according to the present invention has a large pore volume and a large specific surface area, as well as a certain acidic function for acidic cracking reaction, the amorphous silica-alumina of the present invention can provide a carrier or catalyst with excellent properties; specifically, the large specific surface area makes the amorphous silica-alumina capable of supporting a large amount of metal components as well as improving the dispersion of the metal components onto the carrier surface to give full play to the catalyst""s activity, while the large pore volume is beneficial for easy movement of the reactants and products in and out of the cavities of the catalyst, and thus improving the catalyst""s diffusion property during reaction, and the acid sites can serve as the sites of acidic catalytic reaction.
The carrier complex according to the present invention can be used as a main carrier component for supporting the hydrogenation metal component. If the carrier complex contains no zeolite but only the silica-alumina of the present invention as acidic component, the hydrocracking catalyst comprising such a carrier complex belongs to the category of amorphous type hydrocracking catalysts. If the carrier complex contains a comparatively large amount of inert alumina, or has a decreased number of acid sites by moderating the silica content in silica-alumina, it can serve as a carrier of the mild cracking of hydrorefining catalyst.
Therefore, the present invention provides a catalyst comprising (a) active metal component, (b) the silica-alumina of the present invention, (c) optionally a crystalline compound including a zeolite component, and (d) optionally a binder.
In the case of a hydrotreating catalyst, the active metals are hydrogenation metals, which are preferably selected from the group consisting of Groups VIB and VIII metals, more preferably Mo and/or W, and Co and/or Ni. And the metal components are preferably metal oxides, most preferably molybdenum oxide and/or tungsten oxide, cobalt oxide and/or nickelous oxide.
The binder as a component of the catalyst of the present invention can be alumina and/or other small refractory oxide as defined above, preferably a small pore alumina, and more preferably a small pore alumina which is peptized with nitric acid and has a specific surface area of 240-280 m2/g and a pore volume of 0.4-0.5 ml/g.
The crystalline compound including a zeolite as a component of the catalyst of the present invention is that as defined above, preferably a zeolite-Y, and more preferably the modified ultra-hydrophobic zeolite-Y as defined above.
In the most preferable embodiment of the present invention, the catalyst of the present invention is a mid-distillate type hydrocracking catalyst comprising the ultra-hydrophobic zeolite-Y mentioned above as a main acidic component. The acidic property of the zeolite will provide the catalyst with relatively enhanced cracking activity; the large specific surface area and secondary pore structure will improve the dispersion of hydrogenation metals to give full play to the hydrogenation activity, and improve the pore distribution in the catalyst, thus being suitable for cracking oil distillates. In addition, the amorphous silica-alumina according to the invention is used as a supplement acidic component and a main carrier component of the catalyst, so it has a dual-function, i.e., for supplementing the acidic cracking function and serving as a main carrier component for supporting the hydrogenation metals.
The catalyst according to the invention has a specific surface area of 180-300 m2/g, preferably 200-250 m2/g; an IR acidity of 0.25-0.55 mmol/g, preferably 0.35-0.45 mmol/g; and a pore volume of 0.25-0.45 ml/g, preferably 0.3-0.4 ml/g.
In a preferred embodiment of the present invention, the catalyst preferably comprises a Group VIB metal component (calculated as oxide(s)) of 10-40 wt %, a Group VIII metal component (calculated as oxide(s)) of 1-20 wt %, a zeolite-Y of 0-40 wt %, the amorphous silica-alumina of the present invention of 10-70 wt %, and a binder of 0-40 wt %.
More preferably, the catalyst according to the present invention comprises a Group VIB metal component (calculated as oxide(s)) of 10-35 wt %, a Group VIII metal component (calculated as oxide(s)) of 1-15 wt %, a zeolite-Y of 5-40 wt %, the amorphous silica-alumina of 10-60 wt %, and a binder of 5-35 wt %.
Most preferably, the catalyst according to the present invention comprises Group VIB metal oxide(s) of 15-30 wt %, Group VIII metal oxide(s) of 2-10 wt %, the modified ultra-hydrophobic zeolite-Y of 10-30 wt %, the amorphous silica-alumina of 10-50 wt %, and a binder (calculated as dry alumina) of 10-30 wt %.
Most preferably, the catalyst according to the present invention comprises the ultra-hydrophobic zeolite-Y of 15-30 wt %, the amorphous silica-alumina of 20-40 wt %, a binder (calculated as dry alumina) of 15-30 wt %, and Group VIB metal oxide(s) of 18-28 wt % and Group VIII metal oxide(s) of 4-8 wt %.
The catalyst of the present invention can be prepared by a coprecipitation method, a co-mixing method, or an impregnation method.
In an embodiment of the present invention, the catalyst is prepared by an impregnation method, that is, by supporting active metals onto the carrier complex of the present invention by a conventional method such as impregnation to obtain the catalyst of the invention. Specifically, the catalyst of the present invention can be prepared by mixing the amorphous silica-alumina, optionally a crystalline compound including a zeolite, and optionally a binder, kneading, rolling and pressing the blend into block mass, and extrusion moulding the block mass by an extruder into carrier bars; and then supporting active metals onto said carrier to obtain the catalyst of the present invention.
For different purposes of use, the catalyst according to the present invention can be prepared following the above steps and by adjusting the catalyst""s components and the contents thereof.
The formed catalyst can be in any suitable shape, for example, a cylindrical shape having a diameter of 1.2-1.8 mm, or be in a spherical shape or some specific shapes, such as those of trefoil or quatrefoil in cross-section. In general, it is moulded by an extruder into bars.
The preparation process of the catalyst according to the present invention is simple and convenient, easy to operate and suitable for industrial production.
The catalyst of the present invention features that it comprises an acidic amorphous silica-alumina having a large specific surface area and a large pore volume as defined in the present invention. The amorphous silica-alumina of the prior art has relatively small specific surface area and pore volume with the specific surface area rarely being more than 300 m2/g, and in spite of that some have a specific surface area of more than 400m2/g, its specific surface area is contributed by small pore and result in comparatively small pore volume of product. So, when used as the carrier of a catalyst, the amorphous silica-alumina of the prior art needs generally to be combined with xcex3-Al2O3 to support a large amount of metal components. The process for the preparation of the silica-alumina of the present invention employs a specific precipitation method in steps rather than an impregnating method, a pH swinging preparation or other complicated colloid-forming method. The process for the preparation of the silica-alumina of the present invention can provide an amorphous silica-alumina having a large specific surface area and a large pore volume because it features that the formation of undesirable pore structure under the tendency of crystallization is avoided, thus ensuring the effective interaction of silicon and aluminum atoms to provide acid sites as well as a large specific surface area and large pore volume. Moreover, the process according to the present invention is advantageous because it is simple and easy to control, low energy consumption, and needs not specific equipment. The amorphous silica-alumina can have a pore volume of 0.8-1.5 ml/g, and can still have a large specific surface area and large pore volume even in a a very wide range of high SiO2 content. The large specific surface area makes the amorphous silica-alumina capable of supporting a large amount of metal components for hydrogenation, while the acid sites can provide it with adequate cracking activity. The large pore volume is beneficial for easy movement of the reactants and products in and out of the cavities of the catalyst, and thus minimizing the opportunity of secondary cracking reaction, while less carbon deposition will prolong the service life of the catalyst.
When used alone as a support component or catalyst component, the amorphous silica-alumina according to the present invention can also provide a comparatively high acidity. Said amorphous silica-alumina has appropriate acidity and acid strength and can provide relatively moderate cracking activity when matched with the zeolite Therefore, compared with the mid-distillate type hydrocracking catalyst prepared by the prior art, the mid-distillate type hydrocracking catalyst according to the present invention has the features of higher activity and obviously higher mid-distillate selectivity. Compared with the reference catalysts, the catalyst of the present invention exhibits better activity and mid-distillate selectivity in treating the same vacuum gas oils (VGO) under the same conditions.
The most preferable mid-distillate type hydrocracking catalyst according to the present invention is further characterized in that it comprises the ultra-hydrophobic zeolite-Y as mentioned above as a main acidic component. The modified zeolite-Y has an increased molar ratio of SiO2/Al2O3 and a further decreased amount of solid acid. After deeply dealuminized, said modified zeolite-Y has a decreased number of acid sites, and a decreased IR acidity of 0.25-0.55 mmol/g, preferably 0.3-0.5 mmol/g. Compared with the zeolite-Y prepared by the prior art, the zeolite used in the catalyst according to the present invention has a higher crystallinity, a larger specific surface area, and an added number of weak and moderate acid sites being formed with most of them being weak and moderate acid sites desorbed at a temperature ranging from 160 to 450xc2x0 C. and the strong acid sites desorbed at  greater than 450xc2x0 C. being less than 25% (that is, after modified, the acid sites of the zeolite-Y have been decreased very much, but the strong acid sites have not been vanished completely), thus ensuring that no overcracking will occur, while a certain amount of strong acid sites can also ensure adequate cracking activity of the catalyst. The properties of pores, including the larger specific surface area and more secondary pores, shown in the modified zeolite used in the catalyst according to the invention enhance efficiently the hydrogenation activity which is advantageous to the increase in the activity of the ring-opening reaction of multi-ring aromatics or heterocyclics containing nitrogen, and provide more efficient reaction space to meet the requirements of the mid-distillate type hydrocracking catalyst for moderate cracking activity and high hydrogenation activity for cracking heavy hydrocarbon materials.
The catalyst according to the present invention is particularly useful in acidic catalytic reaction, for example, for hydrocracking of petroleum hydrocarbon materials to produce middle distillates. More particularly, the catalyst according to the invention is suitable for treating heavy hydrocarbon materials having a distillation range of 250-600xc2x0 C., generally 300-550xc2x0 C., for example, gas oils, vacuum gas oil distillates, deasphalted oils, cycle oils of FCC, shale oil, coal tars and the like. The hydrocracking reaction according to the invention is generally carried out at a temperature of 340-420xc2x0 C. in the presence of hydrogen under a pressure of 5-30 Mpa, with the H/oil ratio (volume) being 100-5000) and the liquid hourly space velocity (herein after referred to as LHSV) being 0.1-5.0 h1. When the catalyst of the invention is used for treating conventional VGO, the hydrocracking reaction is generally carried out at a temperature of 370-410xc2x0 C. in the presence of hydrogen under a pressure of preferably 10-20 MPa with the H2/oil (volume) ratio being 500-2000 and the LHSV being 0.5-1.5 h.